Cluster storage using subsegmenting for efficient storage

ABSTRACT

Cluster storage is disclosed. A data stream or a data block is received. The data stream or the data block is broken into segments. For each segment, a cluster node is selected, and a portion of the segment smaller than the segment is identified that is a duplicate of a portion of a segment already managed by the cluster node.

CROSS REFERENCE TO OTHER APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 11/824,592, entitled CLUSTER STORAGE USING SUBSEGMENTING FOREFFICIENT STORAGE filed Jun. 29, 2007 which is incorporated herein byreference for all purposes, which claims priority to U.S. ProvisionalApplication No. 60/925,514 entitled SUBSEGMENTING FOR EFFICIENT STORAGE,RESEMBLANCE DETERMINATION, AND TRANSMISSION filed Apr. 19, 2007 which isincorporated herein by reference for all purposes; and claims priorityto U.S. Provisional Patent Application No. 60/923,066 entitled CLUSTERSTORAGE USING SUBSEGMENTING filed Apr. 11, 2007 which is incorporatedherein by reference for all purposes; and claims priority to U.S.Provisional Patent Application No. 60/922,996 entitled CLUSTER STORAGEUSING DELTA COMPRESSION filed Apr. 11, 2007 which is incorporated hereinby reference for all purposes.

BACKGROUND OF THE INVENTION

Scaling data storage systems to hold more information is important asdata storage users continue to increase their desired storagerequirements. One approach is to aggregate multiple individual storagesystems into a cluster that combines the capacity and performance of themultiple individual nodes into one. However, in order to scale smoothly,each node of the cluster must be used appropriately in terms of datastored on the node and processing and throughput required by the node.

Some storage systems optimize storage by eliminating redundant copies ofstored data which is known as deduplication. In some cases, stored datais divided into segments. A new segment that is desired to be stored isfirst compared against those segments already stored. If the segment isalready stored on the system, a reference is stored in place of the newsegment instead of the entire segment. This form of deduplication isreferred to as identity compression.

In using identity compression with a cluster, in order to achieve highefficiency and find a matching segment, each node ideally searches allstored segments in all nodes and in addition can reference, using anindex, all segments in all nodes. The ability to search and index allsegments on all nodes poses problems in scaling to a large number ofnodes because each node must maintain its ability to search and indexover all segments stored on each node of the cluster.

It is useful in scaling storage using a cluster approach to divide thesegments among the nodes so that a single node does not need to maintainits ability to search and index over all segments stored on each node ofthe cluster. Such division is sometimes based on a hash of the segmentso that, given a segment, a hash can be computed and the node that wouldhave the segment, if it already exists in the cluster, can beidentified. Because each node only stores some of the segments, eachnode only needs to index some of the segments. Unfortunately, inassigning segments to different nodes based on a hash of the segment,locality and therefore performance can be lost. Ideally, segmentsaccessed sequentially should be stored sequentially on a disk so that asingle disk access can retrieve many related segments at once. Assigningsequential segments to different nodes makes it difficult, in general,to store the segments sequentially.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention are disclosed in the followingdetailed description and the accompanying drawings.

FIG. 1 is a block diagram illustrating an embodiment of a system forcluster storage using subsegmenting.

FIG. 2 is a block diagram illustrating a storage system using clusterstorage.

FIG. 3A is a block diagram illustrating an embodiment of a data streamor a portion of a data block.

FIG. 3B is a block diagram illustrating an embodiment of a segmentdistributed to a cluster node.

FIG. 4 is a flow diagram illustrating an embodiment of a process forcluster storage.

FIG. 5 is a flow diagram illustrating an embodiment of a process forselecting a storage node.

FIG. 6 is a flow diagram illustrating an embodiment of a process forselecting a storage node.

FIG. 7 is a flow diagram illustrating an embodiment of a process forstoring a representation of a segment.

FIG. 8 is a flow diagram illustrating an embodiment of a process forfinding duplicate subsegments among previously stored subsegments.

FIG. 9 is a flow diagram illustrating an embodiment of a process forstoring a representation of a segment.

FIG. 10 is a flow diagram illustrating an embodiment of a process forstoring a representation of a segment.

DETAILED DESCRIPTION

The invention can be implemented in numerous ways, including as aprocess, an apparatus, a system, a composition of matter, a computerreadable medium such as a computer readable storage medium or a computernetwork wherein program instructions are sent over optical or electroniccommunication links. In this specification, these implementations, orany other form that the invention may take, may be referred to astechniques. A component such as a processor or a memory described asbeing configured to perform a task includes both a general componentthat is temporarily configured to perform the task at a given time or aspecific component that is manufactured to perform the task. In general,the order of the steps of disclosed processes may be altered within thescope of the invention.

A detailed description of one or more embodiments of the invention isprovided below along with accompanying figures that illustrate theprinciples of the invention. The invention is described in connectionwith such embodiments, but the invention is not limited to anyembodiment. The scope of the invention is limited only by the claims andthe invention encompasses numerous alternatives, modifications andequivalents. Numerous specific details are set forth in the followingdescription in order to provide a thorough understanding of theinvention. These details are provided for the purpose of example and theinvention may be practiced according to the claims without some or allof these specific details. For the purpose of clarity, technicalmaterial that is known in the technical fields related to the inventionhas not been described in detail so that the invention is notunnecessarily obscured.

Cluster storage is disclosed. A storage system uses a cluster of nodesto store in-coming data. In-coming data is segmented. Each segment ischaracterized for assignment for storage on a given node. On the givennode of the cluster, segments are stored in a manner that finds andeliminates portions of the segment that are duplicates of data alreadyindexed on the node. Sorting segments into a plurality of nodes reducesthe number of segments to be searched for deduplication and reduces thesize of the index required for a given segment on a node.

In various embodiments, a cluster node is associated with the segmentbased at least in part on a computed hash of all or some of the contentof the segment, on a function of less than all the bytes in the segment(e.g., the initial bytes, the ending bytes, algorithmically determinedsample of bytes, etc.), on hashes computed on subsegments of the segment(e.g., hashes computed on a portion of a segment that is smaller thanthe entire segment), on a sketch of the segment, on a content based tagassociated with the segment, determining which cluster nodes havematches for subsegments of the segment, on node capacities (e.g.,remaining storage capacity, used storage capacity, etc.) orcapabilities, or any other appropriate available resource associatedwith the node. In some embodiments, determining which cluster nodes havematches for subsegments of the segment is based at least in part onhashes of subsegments or a summary data structure such as a Bloomfilter. In some embodiments, a cluster node's capacity or othercapabilities are considered in assigning a segment to a cluster node.

On each node of the cluster, duplicate portions of the segment are foundusing subsegmenting. Subsegmenting allows the use of large segments fordistributing efficiently to nodes and smaller subsegments for efficiencyof compression on a given node while allowing sequentially accessedsubsegments to be stored sequentially. In some embodiments, a subsegmentreference is stored on more than one node so that subsegment referencescan be read sequentially. Subsegmenting efficiently stores segments thatcontain subsegments that are identical to other subsegments by storing areference to identical previously stored subsegments. If a subsegmenthas not been previously stored, the new subsegment is stored.Reconstruction of the segment is enabled by using the references tosubsegments and the newly stored subsegments and information on how toput the subsegments together to make the segment.

In some embodiments, more than one cluster node will include apreviously stored given subsegment. This situation can arise when afirst segment is assigned to a first node and a second segment with anidentical subsegment is assigned to a second node. This enables readingthe first segment more efficiently because reading needs only to takeplace from the first node, and similarly reading the second segmentneeds only to take place from the second node.

In various embodiments, selecting a cluster node is based at least inpart on one or more of the following: one or more segments that arealready stored on the node, one or more similar segments that arealready managed by the node, one or more identical subsegments alreadymanaged by the node, or any other appropriate segment or subsegment tobase a selection of a cluster node.

In some embodiments, the segments and/or subsegments are created basedat least in part on the content of the data in the stream. In someembodiments, they are created using an anchoring function. In variousembodiments, the anchoring function includes computing a hash of asliding window of bytes, determining if the computed hash meets one ormore predetermined criteria, and/or establishing a boundary in analgorithmic manner in or around the sliding window of bytes. In someembodiments, a window is defined and a minimum or maximum value of acomputed function (e.g., a hash or other function) or of a value of dataanywhere within the window is used to define a segment or subsegment. Insome embodiments, a window is defined that includes a plurality ofsubsegments. A hash of the first, all, or a selection of bytes of eachsubsegment is calculated and the maximum or minimum hash value withinthe window is selected to begin a next segment.

FIG. 1 is a block diagram illustrating an embodiment of a system forcluster storage using subsegmenting. In the example shown, storagesystem 100 stores data for clients represented in FIG. 1 by client 112and client 108. A client may have local storage device in addition tolocal memory. For example, client 108 has storage 110 whereas client 112does not have a local storage device. Storage system 100 stores dataeither using internal storage device 102 or attached external storagedevice 104.

Storage system 100 communicates with clients via network 106. Network106 comprises one or more of the following: a local area network, a widearea network, a wired network, a wireless network, the Internet, a fibernetwork, or any other appropriate network enabling communication.Storage system 100 communicates with replica system 120 via network 106as well. Replica system 120 includes internal storage device 122 and isconnected to external storage device 124.

Replica system 120 stores all or a portion of data stored on storagesystem 100. Initially, all or the portion of data stored on storagesystem 100 is replicated on replica system 120 by sending appropriatedata via network 106. After the initial seeding, replica system 120 isupdated by sending from storage system 100 new data. Updating can becontinuous, sent in bursts on a regular schedule, when the amount ofdata exceeds a certain size, or at other appropriate times.

In various embodiments, storage devices 102, 104, 122, and 124 comprisea single storage device such as a hard disk, a tape drive, asemiconductor memory, a plurality of storage devices such as a redundantarray system (e.g., a redundant array of independent disks (RAID)), asystem for storage such as a library system or network attached storagesystem, or any other appropriate storage device or system.

FIG. 2 is a block diagram illustrating a storage system using clusterstorage. In some embodiments, storage system 200 is used to implementstorage system 100 or replica system 120 of FIG. 1. In variousembodiments, replica system 120 receives a data stream, data segments,subsegments that have not previously been stored, and/or references topreviously stored subsegments instead of all segments of a data streamor data block. In the example shown, storage system 200 receives one ormore data streams or data blocks. The data streams or data blocks areprocessed by a plurality of data redirectors, represented in FIG. 2 by202 and 204. A data redirector takes an input data stream or data blockand breaks up the data stream or block into segments. In someembodiments, a segment is created using an anchoring function in which ahash of a sliding window of bytes is computed; if the hash meets somepredetermined criteria, then a boundary between segments is establishedin an algorithmic way in or around the sliding window. In someembodiments, a window is defined that includes a plurality ofsubsegments within which a hash of the first bytes of each subsegment iscalculated and the maximum or minimum hash value within the window isselected to begin a next segment.

In various embodiments, a segment or subsegment boundary is determinedusing a value of a function calculated for a plurality of windows withina segmentation window. A plurality of values are computed that areassociated with candidate boundaries within the segmentation window. Oneof the candidate boundaries is selected based at least in part on acomparison between two or more of the computed values. A boundary withinthe segmentation window is determined. In some embodiments, asegmentation window can be determined by determining a first locationcorresponding to a minimum segment length and determining a secondlocation corresponding to a maximum length where the segmentation windowis the segment from the first location to the second location.Determining a boundary can include determining a plurality of windowswithin the segmentation window. Each window corresponds to a locationwithin the segmentation window and is associated with a candidateboundary. In some embodiments, a function is then evaluated for eachwindow. The function has as its inputs one or more data values of thewindow. In various embodiments, the function comprises a hash function,SHA-1 (Secure Hash Algorithm 1), SHA-256, SHA-384, SHA-512, MD5(Message-Digest algorithm 5), RIPEMD-160 (RACE Integrity PrimitivesEvaluation Message Digest 160-bit version), a Rabin hash, a fingerprint,a CRC (Cyclic Redundancy Check), a sum, an XOR, or any other appropriatefunction to distinguish a window. After the function values aregenerated for all windows, a boundary is selected based at least in parton the values that were generated—for example, the locationcorresponding to an extrema of a function value of all values generated,the location corresponding to the minimum value of all values generatedis selected, the location corresponding to the maximum value of allvalues generated is selected, the location corresponding to a value withthe longest run of 1 bits in its value of all values generated isselected, or the location corresponding to a value with the most 1 bitsin its value of all values generated is selected. If there is tie forthe value, a criteria of selecting the location that maximizes orminimizes the segment length could be adopted.

In the example shown, cluster node 224 includes matching node 206 andstorage device 210; cluster node 226 includes matching node 212 andstorage device 216; cluster node 228 includes matching node 218 andstorage device 222. Each matching node is responsible for managing asubset of the segments stored in the cluster. Managing a segmentincludes enabling finding matches or duplicates for subsegments of thesegment within the subsegments of the other segments being managed, andstoring a deduplicated representation of the segment in a storage node.A segment is transmitted to one or more matching function nodes,represented in FIG. 2 by 206, 212, and 218, of a cluster node,represented in FIG. 2 by 224, 226, and 228, respectively. In someembodiments, the assignment to one or more matching nodes is a functionof the hash computed as part of the anchoring function. In someembodiments, the assignment is based on a function of less than all ofthe bytes in the segments. For example, it could be based on a functionof the initial bytes of the segment, of the ending bytes of the segment,or some algorithmically determined sample of the bytes. In someembodiments, the assignment is based on one or more tags of the segment.In various embodiments, a tag comprises a summary feature set, a sketch,a hash or fingerprint of some or all of the segment or the subsegmentsof segment, or any other appropriate characterizer of the segment thatcan be used for assigning the segment to a cluster node. In someembodiments, a summary feature set is determined by selecting aplurality of either fixed length or variable length parts or shingles ofa first segment; for each shingle, computing a plurality of values byapplying a set of functions to each shingle; and from all the valuescomputed for all the shingles, selecting a first subset of values. Insome embodiments, the first subset of values is used in determiningresemblance between the first segment and a second segment. In someembodiments, other external factors, such as bytes in neighboringsegments or other available resources in a node are used to assign thesegment to a matching function node. In some embodiments, the assignmentis based on sending one or more tags of the segment to some or all ofthe matching nodes to determine if the matching node is likely to beable to identify duplicate portions of data or duplicate subsegments. Insome embodiments, the assignment is based on data maintained in the DataRedirectors about the segments stored on each node such as a summarydata structure—for example, a Bloom filter. In some embodiments, afunction generates a value for each segment and the Data Redirectorsmaintain a table which maps a set of such values to each node and asegment is assigned to a node at least in part based on the mapping insuch a table.

In some embodiments, the one or more matching function nodes havealready stored a similar or identical segment. The segment is broken upinto subsegments and the matching function node looks for matchingsubsegments within all or part of the data stored associated with thematching node. In some embodiments, the part of the data within whichthe subsegments are searched for includes previously stored segmentsthought to be similar to the segment.

In some embodiments, multiple matching nodes may be hosted on the samephysical storage device.

FIG. 3A is a block diagram illustrating an embodiment of a data streamor a portion of a data block. In the example shown, data stream orportion of a data block 300 is shown. Data stream or portion of a datablock 300 can be data that is being backed up, data that is beingstored, data that is being replicated on a remote site, or any otherappropriate data stream or portion of a data block.

FIG. 3B is a block diagram illustrating an embodiment of a segmentdistributed to a cluster node. In some embodiments, cluster nodes 316,318, and 320 are similar to cluster nodes 224, 226, and 228 of FIG. 2.In the example shown, data stream or portion of a data block issegmented into a plurality of segments—for example, segments 310, 312,and 314. Segmenting of the data stream or portion of the data block canuse content-based determination of segment boundaries (e.g., hash ofcontent in a window is equal to a value, or hash of content in a windowis the minimum or maximum of the hashes of the content of a set ofwindows), non-content based determination of segment boundaries (e.g.,byte count), file-based segment boundaries, or any other appropriate wayof breaking the data stream or data block into segments. In variousembodiments, segments are the same size or are different sizes. Invarious embodiments, the segments may be non-overlapping or overlapping.Segments 310, 312, and 314 are distributed to cluster nodes 316, 318,and 320, respectively. Distribution of a segment to a cluster node isbased on the segment content, segment number, metadata associated withthe segment, and/or a cluster node having likely similar segments sothat efficient storage of the segment can take place. In someembodiments, a tag or other characterization of a segment is distributedto a plurality of nodes, and a given node having likely similar segmentscan indicate that it would be a good candidate node for the segment tobe distributed to.

FIG. 4 is a flow diagram illustrating an embodiment of a process forcluster storage. In some embodiments, the process of FIG. 4 isimplemented in storage system 200 of FIG. 2. In the example shown, in400 a data stream or data block is received. In 402, the data stream ordata block is broken into segments. In 404, a first segment is selected.In 406, a storage node is selected. In 408, a portion of a segment thatis a duplicate of a portion of a previously stored segment isidentified; a representation of the portion is stored; and data that isnot a duplicate of previously stored data is stored. In 410, it isdetermined if there are more segments to process. If so, then in 412 anext segment is selected and control passes to 406. If not, then theprocess ends.

FIG. 5 is a flow diagram illustrating an embodiment of a process forselecting a storage node. In some embodiments, the process of FIG. 5 isused to implement 406 of FIG. 4. In the example shown, in 500 a tag iscomputed. In 502, a node is selected using the tag. In some embodiments,the segment is assigned to a node based on the tag without considerationof what segments are currently stored in the node; for example, all oddtags (e.g., a hash value) go to node 1, even tags go to node 2. Overtime the nodes will have similar segments, but there is actually nocheck for having similar segments when the node is selected. In someembodiments, a redirector accesses a database or table which maps setsof tag values to each node to determine to which node to assign thesegment. In some embodiments, a given node's loading and/or capacityis/are considered in assigning a segment to a given node. In variousembodiments, the tag comprises a sketch, a hash, or any otherappropriate manner of identifying likely similar segments.

In some embodiments, a redirector compares the tag to a summary datastructure (e.g., a Bloom filter) that the redirector is maintaining todetermine which node to assign a given segment to.

FIG. 6 is a flow diagram illustrating an embodiment of a process forselecting a storage node. In some embodiments, the process of FIG. 6 isused to implement 406 of FIG. 4. In the example shown, in 600 a tag iscomputed. In 602, the tag is broadcast to all nodes. In someembodiments, the tag is sent to one or more nodes but not all nodes. Insome embodiments, the nodes selected to receive the tag are based atleast in part on the tag. In 603, the nodes determine whether theycontain a likely similar segment. The nodes could use a Bloom filter todetermine if they have similar segments, or they could actually identifyduplicate subsegments. In 604, an indication is received that one ormore nodes likely contain(s) similar previously stored segment(s). In606, a node is selected based on the indication. In some embodiments,the indication indicates a measure of how many likely similar storedsegments are stored on a node. In some embodiments, the indicationindicates the number of subsegments which match subsegments stored on anode. In some embodiments, the indication includes information regardingthe overall number of stored segments at a given node so that loadbalancing can be considered in determining assignment of a segment. Invarious embodiments, the tag comprises a sketch, a hash, or any otherappropriate manner of identifying likely similar segments.

FIG. 7 is a flow diagram illustrating an embodiment of a process forstoring a representation of a segment. In some embodiments, the processof FIG. 7 is used to implement 408 of FIG. 4. In the example shown, in700 the segment is sent to the selected node. In 702, the segment isreceived at the selected node. In 704, the segment is broken intosubsegments. In 706, tags, which include fingerprints, for subsegmentsare calculated. In 708, reference(s) to previously stored subsegment(s)and/or segment data are identified using tags. In some embodiments,fingerprints are used to identify determine if the subsegment is aduplicate of a previously stored subsegment. In some embodiments, tagsare also used to identify subsegments that are not duplicates and needto be stored. In 710, associated tags and segments are stored usingidentified reference(s) and/or segment data.

FIG. 8 is a flow diagram illustrating an embodiment of a process forfinding duplicate subsegments among previously stored subsegments. Insome embodiments, the process of FIG. 8 is used to implement 708 of FIG.7. In the example shown, in 800 a first subsegment is selected. In 802,it is determined if the selected subsegment is a duplicate of apreviously stored subsegment. In some embodiments, the selectedsubsegment is determined to be a duplicate or not of a previously storedsubsegment using fingerprints. If the selected subsegment is aduplicate, then in 804 the subsegment is identified as identical andcontrol passes to 808. If the selected subsegment is not a duplicate,then in 812 subsegment data and associated tags (e.g., which includefingerprints) are identified as not duplicate, if appropriate, andcontrol passes to 808. In some embodiments, the identified subsegmentdata and associated tags are stored to be used for reconstruction of thesegment. In some embodiments, in cases where a sliding window is used toidentify subsegments, then it may not be necessary to store a givenselected subsegment and associated tags. In 808, it is determined ifthere are more subsegments. If there are more subsegments, then a nextsubsegment is selected in 810 and control passes to 802. If there arenot more subsegments, then the process ends.

FIG. 9 is a flow diagram illustrating an embodiment of a process forstoring a representation of a segment. In some embodiments, the processof FIG. 9 is used to implement 408 of FIG. 4. In the example shown, in900 the tag is sent to the selected node. In 902, the tag is received atthe selected node. In 904, likely similar segments are identified usingthe tag. In 906, tags are acquired for the likely similar segments. Insome embodiments, tags include fingerprints. In various embodiments, thetags are read from the selected node's storage or the tags arecalculated on the fly as needed. In some embodiments, the tags arestored together for convenient and fast acquisition. In 908, tags aresent from selected node. In 910, tags are received from selected node.In 912 the segment is broken into subsegments. In 914, tags arecalculated for the subsegments. In 916, reference(s) to previouslystored subsegment(s) and/or segment data are identified using tags. Insome embodiments, fingerprints are used to determine if a subsegment isa duplicate of a previously stored subsegment. In 918, the reference(s)and/or segment data and associated tags are sent to the selected node.In 920, the reference(s) and/or segment data and associated tags arereceived at the selected node. In 922, store associated tags and segmentusing reference(s) and/or segment data.

FIG. 10 is a flow diagram illustrating an embodiment of a process forstoring a representation of a segment. In some embodiments, the processof FIG. 10 is used to implement 408 of FIG. 4. In the example shown, in1000 the segment is broken into subsegments. In 1002, tags arecalculated for the subsegments. In some embodiments, the tags includefingerprints. In 1004, tags are sent to selected node. In 1006, tags arereceived at selected node. In 1008, likely similar segments areidentified using tags. In 1010, tags are acquired for likely similarsegments. In some embodiments, tags include fingerprints. In variousembodiments, the tags are read from the selected node's storage or thetags are calculated on the fly as needed. In some embodiments, the tagsare stored together for convenient and fast acquisition. In 1012,reference(s) to previously stored subsegment(s) and/or segment data areidentified using tags. In some embodiments, fingerprints are used todetermine if a subsegment is a duplicate of a previously storedsubsegment. In 1014, reference(s) to segment data is/are sent fromselected node. In some embodiments, tags are used to reference segmentdata. In some embodiments, subsegment tags are sent from the node asreferences to subsegments. In 1016, reference(s) to segment data is/arereceived from selected node. In 1018, segment data is sent to selectednode. In 1020, segment data is received at selected node. In 1022,associated tags and segment are stored using reference(s) and/or segmentdata.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, the invention is not limitedto the details provided. There are many alternative ways of implementingthe invention. The disclosed embodiments are illustrative and notrestrictive.

What is claimed is:
 1. A system, comprising: a plurality of data storage systems; a processor configured to: break a data stream or a data block into a plurality of segments that includes at least a first segment; compute a tag for the first segment, wherein the tag comprises a summary feature set, a sketch, a hash or a fingerprint for at least a portion of the first segment; send the tag to each data storage system of at least a subset of the plurality of data storage systems, wherein a data storage system of the at least the subset of the plurality of data storage systems that receives the tag determines, based at least in part on the tag, whether the data storage system of the at least the subset of the plurality of data storage systems contains at least one segment that is similar to the first segment or at least one subsegment that is identical to a subsegment of the first segment; receive an indication from each data storage system that includes a measure of at least one of: a number of similar segments stored at each data storage system, a number of identical subsegments stored at each data storage system, or a total number of segments stored at each data storage system; select a specific data storage system of the at least the subset of the plurality of the data storage systems to store the first segment based at least in part on the indication; determine whether a portion of the first segment that is smaller than the first segment is a duplicate of a portion of a second segment stored at the specific data storage system; and store the first segment at least in part by storing a representation of the duplicate portion of the first segment; and a memory coupled to the processor and configured to provide the processor with instructions.
 2. A system as in claim 1, wherein each data storage system includes a summary data structure that is used to determine whether the data storage system of the at least the subset of the plurality of data storage systems contains at least one similar segment or one identical segment.
 3. A system as in claim 1, wherein the data stream associated with the first segment comprises one or more of the following: a file, a plurality of files that are related to each other, a directory of files, or a plurality of segments that are related to each other.
 4. A system as in claim 1, wherein the data stream is associated with the first segment by providing an indication identifying the data stream to the specific data storage system storing the segment.
 5. A system as in claim 4, wherein segments associated with the data stream that are caused to be stored on the specific data storage system are caused to be stored by causing one or more subsegments to be stored, and wherein the segments associated with the data stream that are caused to be stored on the specific data storage system such that the segments can be retrieved together efficiently.
 6. A system as in claim 1, wherein the processor is further configured to store the first segment using segment data that is not a duplicate of previously stored data.
 7. A system as in claim 1, wherein the processor is further configured to find duplicates for a second portion of the first segment within other segments being managed by the plurality of data storage systems.
 8. A system as in claim 1, wherein the specific data storage system manages a subset of the segments stored in the plurality of data storage systems.
 9. A system as in claim 1, wherein determining that the portion of the first segment smaller than the first segment is the duplicate of the portion of the specific data storage system stored segment includes breaking the first segment into a plurality of subsegments and identifying one subsegment of the plurality of subsegments that has already been stored by the specific data storage system.
 10. A system as in claim 1, wherein a subsegment reference is stored on more than one data storage system so that subsegment references can be read sequentially.
 11. A system as in claim 1, wherein the portion of the segment smaller than the segment is stored on more than one data storage system of the plurality of data storage systems so that the portion of the segment can be read sequentially.
 12. A method as in claim 1, wherein breaking the data stream or the data block into segments is based at least in part on content of the data stream or the data block.
 13. A system as in claim 1, wherein breaking the data stream or the data block into segments is based at least in part on file boundaries within the data stream or the data block.
 14. A system as in claim 1, wherein breaking the data stream or the data block into segments is based at least in part on an anchoring function, wherein the anchoring function includes determining if the computed hash meets one or more predetermined criteria.
 15. A system as in claim 1, wherein breaking the data stream or the data block into segments is based at least in part on an anchoring function, wherein the anchoring function includes uses a value of a function calculated for a plurality of windows within a segmentation window.
 16. A method, comprising: breaking a data stream or a data block into a plurality of segments that includes at least a first segment; computing, using a processor, a tag for the first segment, wherein the tag comprises a summary feature set, a sketch, a hash or a fingerprint for at least a portion of the first segment; sending the tag to each data storage system of at least a subset of the plurality of data storage systems, wherein a data storage system of the at least the subset of the plurality of data storage systems that receives the tag determines, based at least in part on the tag, whether the data storage system of the at least the subset of the plurality of data storage systems contains at least one segment that is similar to the first segment or at least one subsegment that is identical to a subsegment of the first segment; receiving an indication from each data storage system that includes a measure of at least one of: a number of similar segments stored at each data storage system, a number of identical subsegments stored at each data storage system, or a total number of segments stored at each data storage system; selecting a specific data storage system of the at least the subset of the plurality of the data storage systems to store the first segment based at least in part on the indication; determining whether a portion of the first segment that is smaller than the first segment is a duplicate of a portion of a second segment stored at the specific data storage system; and storing the first segment at least in part by storing a representation of the duplicate portion of the first segment.
 17. A computer program product, the computer program product being embodied in a non-transitory computer readable medium and comprising computer instructions for: breaking a data stream or a data block into a plurality of segments that includes at least a first segment; computing a tag for the first segment, wherein the tag comprises a summary feature set, a sketch, a hash or a fingerprint for at least a portion of the first segment; sending the tag to each data storage system of at least a subset of the plurality of data storage systems, wherein a data storage system of the at least the subset of the plurality of data storage systems that receives the tag determines, based at least in part on the tag, whether the data storage system of the at least the subset of the plurality of data storage systems contains at least one segment that is similar to the first segment or at least one subsegment that is identical to a subsegment of the first segment; receiving an indication from each data storage system that includes a measure of at least one of: a number of similar segments stored at each data storage system, a number of identical subsegments stored at each data storage system, or a total number of segments stored at each data storage system; selecting a specific data storage system of the at least the subset of the plurality of the data storage systems to store the first segment based at least in part on the indication; determining whether a portion of the first segment that is smaller than the first segment is a duplicate of a portion of a second segment stored at the specific data storage system; and storing the first segment at least in part by storing a representation of the duplicate portion of the first segment. 